This application is not referenced in any microfiche appendix.
1. Field of the Invention
This invention relates to a low NOX burner for combustion of air and fuel gas.
2. Description of the Related Art
Fuel gas is burned by mixing it with air in the combustion process. Oxygen from the air is combined with the fuel gas that contains combustible components. If the gas is thoroughly mixed with the air and combustion occurs under ideal conditions, the results of the combustion will consist primarily of carbon dioxide, water vapor and nitrogen. Carbon dioxide, water vapor, or nitrogen are not generally harmful to the environment. When a gas burns in a high temperature environment, portions of the nitrogen and oxygen in the atmosphere react to produce oxides of nitrogen (NOX). As a general principle, NOX production increases as combustion temperature increases. Oxides of nitrogen are generally considered environmental hazards in the atmosphere.
Methods and apparatus to suppress the formation of NOX have been developed and used heretofore. A common apparatus for reducing the formation of NOX is a staged air burner apparatus. In a staged air burner apparatus a first portion of combustion air is introduced into a first zone to produce a reducing environment that suppresses NOX formation and the remaining portion of air is introduced into a second zone. Methods and apparatus have also been developed wherein all the combustion air and some of the fuel is introduced in a first zone with the remaining fuel being introduced into a second zone in a staged fuel approach. An excess of air in the first zone acts as a diluent which lowers the temperature of the burning gases and thereby reduces the formation of NOX. Other methods and apparatus have been developed wherein flue gases are combined with the fuel/air mixtures to dilute the mixtures and thereby lower the combustion temperatures and formation of NOX.
While the prior methods and burner apparatus for producing flue gases having low NOX contents have achieved varying degrees of success, there still remains a need for improvement in such methods and burner apparatus whereby low NOX content flue gases are produced by a simple, economical burner apparatus.
The present invention is an improved burner for combustion of fuel gas with air in a manner to result in low NOX formation. The burner is generally circular and has a refractory tile and gas tips. The burner apparatus bums fuel gas and furnace gases mixed with air to form low NOX content in a furnace flue gas.
Because of the position of the gas tip within the burner tile, all the fuel gas is mixed with the furnace flue gas. The fuel gas tips are spaced around the outer circumference of a generally circular passageway in the burner tile. Each gas tip is positioned to cause the fuel gas to entrain furnace flue gas. Each tip may be set within the burner tile opening or set back from the opening. The spacing of the gas tips about the circumference of the opening may be symmetrical or asymmetrical. Gas tip elevation may be above, below or flush with the burner tile.
The burner tile has a top and protrusions rising from the top. The protrusions are spaced apart to form a channel along the burner tile top. Each fuel gas tip has multiple ports, at least an ignition port and a firing port. The ignition port injects fuel gas through the passageway made by the protrusions rising from the top of the burner tile. This produces combustion within an ignition zone located on top of the tile.
The firing port injects fuel gas in a direction that is generally upward, with respect to the pathway of ignition port. This causes the fuel gas to penetrate and entrain combustion products from the flue gas. The resulting mixture of fuel gas and flue gas is directed out of the burner tile to mix with combustion air that is discharged through the burner tile.
In the present invention, liquid fuel or a mixture of gas and liquid fuel may be used as well as gas fuel. The discharge of the fuel from either port may be synchronous or asynchronous with respect to other ports or gas tips.
The use of a single gas tip and fuel gas supply pipe for a firing and ignition port, rather than having separate gas tips and piping, is a more economical design.
The arrangement of the firing ports helps to entrain a mixture of air and combustion products from the ignition zone, to provide a cooler temperature burning in the combustion zone.
Other objects and further scope of the applicability of the present invention will become apparent from the detailed description to follow, taken in conjunction with the accompanying drawings wherein like parts are designated by like reference numerals.